1. Field of the Invention
Grounded submarine electric power cables.
2. Description of the Prior Art
Normally, electric power cables are manufactured in relatively short lengths with a conductive sheath of lead or aluminum provided which is grounded at each cable joint. The grounding is necessary in order to prevent excessive current and voltage build up in the metal sheath. When long submarine power cables are manufactured they are usually made in one piece, thus it is necessary to ensure that the metal sheath is grounded either continuously or at specified intervals.
The problem which is encountered in obtaining the desired grounding concerns the penetration of the corrosion protective insulating plastic sheath which covers the metal sheath. One of the methods and means used in the prior art is described in U.S. Pat. No. 3,810,729. That patent describes conventional penetration methods and their drawbacks. The teaching of the prior art patent is to use a screw and nut device with the nut part secured to the metal sheath or to a frettage applied over the metal sheath. The device includes a C-shaped clamping element mounted on the frettage and covered by an insulating sheath except for a small hole over a threaded hole in the clamping element which includes a threaded element extending through the sheath hole and into the threaded hole of the clamping element. The threaded element may have arms or spokes to assist in screwing it into place. The threaded element is covered by and in contact with the surrounding armor. Clamping elements are applied to the frettage prior to the extrusion of the insulating sheath thereover and holes are successively punched into the sheath over the threaded hole in the clamping element. Then the threaded elements are successively inserted and thereafter the armor is applied. The hole made in the plastic sheath is said to be sealed by squeezing the plastic sheath between the nut and screw.
It is very unlikely that the described means and method for grounding the metal sheath will work satisfactorily in practice since the cable is coiled, bent and unbent many times during the installation. The stiff mechanical connection is likely to be easily damaged or broken and the hole through the plastic sheath may easily be torn or stretched with the result that the sealing may be impaired.
In U.S. Pat. No. 3,801,729, a conventional method employing a single conductive element having a dimension of sufficient height to extend through the thickness of the insulating sheath is described which comes into contact with the armor. This patent recognized that such a means and method has the drawback of removing and subsequently reconstructing portions of the sheath at each place where the grounding device is provided.